Field of the Invention
The present invention relates to a power supply circuit and, more particularly, to a power supply protection circuit and a method.
Description of the Related Art
In a constant voltage output power supply circuit, an output feedback terminal FB samples output voltages by voltage-dividing resistors R1 and R2. An output current is regulated to make the voltage of the output feedback terminal FB be equal to a reference voltage in a current control unit, so as to regulate the output voltage to make it be stabilized at a preset voltage.
As shown in FIG. 1, the constant voltage output power supply circuit 100 includes a current control unit 11 and a voltage feedback unit 12. The voltage feedback unit 12 consists of a first resistor R1 and a second resistor R2 connected in series. A common point of the first resistor R1 and the second resistor R2 is a feedback terminal FB of an output voltage Vout, and the feedback terminal FB of the output voltage Vout is connected to the current control unit 11. The current control unit 11 includes a second operational amplifier U2, a first input terminal of the second operational amplifier U2 is connected to the feedback terminal FB, and a second input terminal is connected to a second reference signal Vref2. The second reference signal Vref2 is compared with a feedback voltage VFB, and the circuit is controlled according to the comparison result thus to realize the constant voltage output.
However, when an output load is short-circuited, the output feedback voltage VFB is about 0V. Since the current control unit 11 takes samples and detects that the output feedback voltage VFB is lower than the second reference signal Vref2, the output current increases to reach the maximum output current of the constant voltage output power supply circuit 100. Since the output voltage is near 0 when the load is short-circuited, although the output current reaches the maximum output current, output power of the circuit may still be within the normal work range, and the constant voltage output power supply circuit will not be damaged due to overlarge power consumption.